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Question

Phenolphthalein indicator is colourless in an acid and turns pink in an alkaline solution. When an aqueous solution of potassium iodide is electrolysed with phenolphthale in indicator, what colours appear at the electrodes?
Cathode: 2H2O(l)+2eH(g)+2OH(aq)
Anode: 2I(aq)I2(s)+2e

A
Brown at the cathode and pink at the anode
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B
Red at the cathode and pink at the anode
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C
Brown at the anode and colourless at the cathode
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D
Pink at the cathode and brown at the anode
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Solution

The correct option is C Pink at the cathode and brown at the anode
Cathode: 2H2O+2eH(g)+2OH
Here OH is alkaline so phenolphtale is turned pink.
Anode: 2II2(s)+2e
I+I2I3
This is the reason for brown colour in anode.

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